Why this could be useful:
3rd party applications that maintain user accounts would be enabled to create new wiki users without manual interaction. E.g. providing a centralized documentation platform with acl for a large number of users.

Current workflow:
Export users to csv and then import with usermanager mass import feature. After import the users acl are modified by the workflow using xmlrpc plugin.acl.addAcl . Deleting is also done via xmlrpc dokuwiki.deleteUsers

Proposal:
Add dokuwiki.addUser xmlrpc function.
Name: dokuwiki.createUser
Parameters: (string)username, (string)fullname, (string)email, (array)groups, (string)password (optional),(boolean)send_mail
Description: Adds a new user. When no password is provided the system generates a new one. When send_mail is true the user get's an account notification by mail.